Software Design Methodology

328 Chapter 12. Model-Based Analysis: The HASARD Method

12.4.3 Analysis of quality features

From the quality model in Figure 12.13, we can derive a number of quality features

of the client-server architecture of websites.

For example, we can derive the contribution factors to a number of quality

attributes. For instance, the navigability of the HTML files depends on the

following factors:

• the complexity of the HTML files;

• the property of well structured HTML files with reasonable sizes;

• the HTML file’s correctness in terms of the hyperlinks are indicative;

• the availability of site map;

• the availability of the online help system.

Similarly, we can derive that the user gets correct information depending on

the following factors:

• the HTML files are correct in terms of the contents are correct;

• the data files are correct in terms of their contents are correct;

• the server hardware and software do not fail;

• the HTML files are up to date, which is updated timely by the server;

• the Internet delivers the messages correctly.

The performance of the server depends on the load on the server, which in

turn depends on the following factors:

• the number of requests made by the clients;

• the server’s computational capability and resources;

• the security of the server in sense of the possibility of being attacked by

hackers;

Software Design Methodology 329

• the correct behaviour of the Internet in terms of duplicated messages

delivered.

From the quality model, we can also derive the main risks of the architectural

design, which include:

• the use of a new format of data file could cause the information not to be

displayed in the client computer;

• the compatibility problem of the client code may mean that the system

could not be executed on the client’s computer, and consequently, the

system unusable;

• the heavy traffic on the Internet may hinder the usability of the system;

• hackers’ attacks may cause the system’s poor performance, and in extreme

cases, the systems clash, information leak, data integrity be damaged when

HTML/Data files are removed or replaced with incorrect ones, etc.

• poor indicative hyperlinks may cause bad navigability, which in turn hinder

the user to find required information; etc.

The main trade-off point in the design of a website is the decomposition of

information into HTML files. Too many HTML files may cause a complexity in

the hyperlink network. However, too few HTML files may cause large files to be

transmitted over the Internet and result in poor responsiveness.